Silicon-based single sideband modulator chip with low driving voltage and high sideband rejection ratio

Abstract

The invention relates to a silicon-based single-sideband modulator chip with low driving voltage and high sideband rejection ratio. The silicon-based single-sideband modulator chip comprises a first end face coupler, a second end face coupler, a single-sideband modulator module, a first-stage unequal-ratio beam splitter, a monitoring detector and a silicon optical switch. On the basis of the plasma dispersion effect of a silicon-based photoelectron chip in principle, the phase of the modulator is efficiently regulated and controlled through carrier injection through a carrier injection type modulator structure, the working swing of the single-sideband modulator is reduced, and meanwhile the high sideband rejection ratio is kept; on the system level, a thermo-optic phase shifter is arranged in the single-sideband modulator to be matched with an external monitoring detector to achieve accurate regulation and control of phases, and meanwhile, a beam splitter is arranged to enable the single-sideband modulator to be compatible with on-chip and off-chip applications. The circuit is simple in design, can reduce the power consumption and cost and improve the integration level compared with a traditional scheme, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the fields of electro-optical modulation technology and silicon-based optoelectronic technology, in particular to a silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio. Background Art

[0002] Satellite laser communication is limited by the size, power consumption, and mass of the satellite platform. Traditional single-sideband modulators are difficult to meet usage requirements due to their high driving voltage and high power consumption. In addition, optical fiber-structured laser communication has certain limitations in size and complexity.

[0003] Silicon-based optoelectronic chips, thanks to their CMOS compatibility, enable low-cost, large-scale production, while also offering advantages such as high integration, high reliability, and low power consumption. However, most modulators in currently available literature utilize conventional bulk lithium niobate or silicon-based carrier-depletion structures. For example, the single-sideband modulator with ultra-high sideband suppression ratio based on a carrier-depletion modulator in the prior art [A Silicon Optical Single Sideband Modulator With Ultra-High Sideband Suppression Ratio," in IEEE Photonics Technology Letters, vol. 32, no. 16, pp. 963-966, 15Aug. 15, 2020] is prepared based on a silicon-based optoelectronic process platform and is also based on the principle of plasma dispersion. Due to its low modulation efficiency, Vpi·L ​​is 2V·cm, and the modulator length needs to be 1mm to achieve a Vpi of 20V. Therefore, it is difficult to achieve a good modulation depth, resulting in a low optical output power of the required sideband. In addition, traditional discrete devices are difficult to meet the strict requirements of satellite platforms for volume, power consumption and quality, and optical fiber solutions face the challenges of system complexity and insufficient integration. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of traditional discrete devices used for single-sideband modulators, such as large size and high power consumption. A silicon-based single-sideband modulation chip with low driving voltage and high sideband suppression ratio is proposed. It adopts a carrier injection structure, combined with a thermo-optical phase shifter and an on-chip monitoring detector to achieve efficient phase control and precise operating point locking.

[0005] The technical solutions of the present invention are as follows:

[0006] A silicon-based single-sideband modulator chip with low drive voltage and high sideband suppression ratio, including a first end coupler, a second end coupler, a single-sideband modulator module, a first-stage unequal beam splitter, a monitoring detector, and a silicon optical switch. Its connections are as follows:

[0007] The first end face coupler of the single-sideband modulator chip is connected to the single-sideband modulator module, followed by a first-stage unequal-splitting beam splitter. The low-splitting ratio end of the unequal-splitting ratio beam splitter is connected to a monitoring detector, and the high-splitting ratio end is connected to a silicon optical switch. The single-sideband modulated signal is then output through the second end face coupler.

[0008] The single-sideband modulator module includes a first beam splitter, a first carrier injection modulator, a second carrier injection modulator, a first thermo-optical phase shifter, a second thermo-optical phase shifter, a first beam combiner, a second beam combiner, a third thermo-optical phase shifter, and a third beam combiner.

[0009] The single-sideband modulator module receives the signal light input by the first end coupler, splits it through the first beam splitter, and inputs it into the first carrier injection modulator and the second carrier injection modulator respectively. The overall working point is controlled by the thermo-optical phase shifter, wherein the first thermo-optical phase shifter controls the first carrier injection modulator so that its two arms have a phase difference of 180° and are combined through the first beam combiner. At the same time, the second thermo-optical phase shifter controls the second carrier injection modulator so that its two arms also have a phase difference of 180° and are combined through the second beam combiner. Finally, the third thermo-optical phase shifter is used to make the phase difference of the two arms 90° and combine them through the third beam combiner. At this time, the entire single-sideband modulator is at the NULL point. At this time, a single-sideband frequency-shifted signal with a high sideband suppression ratio can be generated by inputting two orthogonal signals into the first carrier injection modulator and the second carrier injection modulator respectively.

[0010] In the single-sideband modulator module (3), the input optical signal is modulated by the single-sideband modulator, and the output signal satisfies the following formula:

[0011] Eout=Ein / 2*((e jφ1(t) +e jφ2(t) )

[0012] When φ1(t) = φ2(t) in frequency, but the phase difference is 90°, a larger sideband suppression ratio can be generated. After considering the modulator's half-wave voltage, drive voltage, splitting ratio and other factors, the output should satisfy the following formula:

[0013] E out =2*E in [γe jφ1(t) +((1-γ)e jφ2(t) ]·e jΔθ

[0014] The carrier injection modulators used in the described single-sideband modulator module are all manufactured using CMOS technology and adopt a single-ended push-pull structure. The central region is heavily N-type doped with a doping concentration greater than 1e20, and the electrode doping region is heavily P-type doped with a doping concentration greater than 5e20. To achieve a compromise between high modulation efficiency and low insertion loss, a medium-doped region with a doping concentration of 1e18 is added, which has a small overlap with the light transmission waveguide region. To achieve terminal matching of high-speed signals, the terminal resistor is made of TiN material with a resistance of 50 ohms, and the single-ended push-pull electrode requires differential impedance matching.

[0015] The advantages of the present invention are:

[0016] Compared with bulk lithium niobate modulators and silicon-based carrier depletion modulators, the present invention has significantly improved modulation efficiency, insertion loss and volume. The standard size of the depletion modulator is above 4 mm, while the present invention is only 300 microns, which is an order of magnitude smaller. In terms of modulation efficiency, the Vpi of the present invention is only 1V, compared with the other two devices whose Vpi are both above 5V, which is a significant improvement.

[0017] The process of the present invention is simple, and the sideband suppression ratio can reach more than 30dB. It is based on silicon-based optoelectronic technology and integrates other devices such as on-chip detectors. It can be used off-chip through thermo-optical switching steps, while meeting the frequency shifting within the chip, effectively reducing the system's space, power consumption, and cost, and greatly improving the system's stability and anti-interference performance. It has great application prospects in the fields of on-chip frequency shifting, homodyne demodulation and phase locking. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the overall structure diagram of a silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio in the present invention.

[0019] Figure 2 This is a schematic diagram of the structure of the single sideband modulator module in a silicon-based single sideband modulator chip with low driving voltage and high sideband suppression ratio of the present invention.

[0020] Figure 3 This is a schematic diagram of the structure of a carrier injection modulator in a silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to examples and drawings, but the scope of protection of the present invention should not be limited thereto.

[0022] Figure 1This is the overall structure diagram of a silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio of the present invention, including a first end coupler 1, a second end coupler 2, a single-sideband modulator module 3, a first-stage unequal-splitting beam splitter 4, a monitoring detector 5, and a silicon optical switch 6.

[0023] The first end face coupler 1 of the single sideband modulator chip is connected to the single sideband modulator module 3, followed by the first stage unequal splitting ratio beam splitter 4. The low splitting ratio end of the unequal splitting ratio beam splitter is connected to the monitoring detector 5, and the high splitting ratio end is connected to the silicon optical switch 6, and then the single sideband modulated signal is output through the second end face coupler 2.

[0024] The end coupler is used to achieve low-loss coupling of external light source signals and output of single-sideband frequency-shifted signal light after modulation, wherein the first end coupler 1 serves as an input end coupler and the second end coupler 2 serves as an output end coupler.

[0025] The monitoring detector 5 is used to detect the partial optical signal after the splitting and feedback the modulation status;

[0026] The silicon optical switch 6 is used to control the flow direction of the single-sideband modulated signal to control its full or partial output to the outside or inside the chip.

[0027] Figure 2 It is a structural schematic diagram of a single-sideband modulator module in a silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio of the present invention, including a first beam splitter 3-1, a first carrier injection modulator 3-2, a second carrier injection modulator 3-3, a first thermo-optical phase shifter 3-4, a second thermo-optical phase shifter 3-5, a first combiner 3-6, a second combiner 3-7, a third thermo-optical phase shifter 3-8, and a third combiner 3-9.

[0028] The single-sideband modulator module 3 receives the signal light input by the first end coupler 1, splits it through the first beam splitter 3-1, and inputs it into the first carrier injection modulator 3-2 and the second carrier injection modulator 3-3 respectively. The overall working point is controlled by the thermo-optical phase shifter, wherein the first thermo-optical phase shifter 3-4 controls the first carrier injection modulator 3-2 so that its two arms have a phase difference of 180° and are combined through the first beam combiner 3-6. At the same time, the second thermo-optical phase shifter 3-5 controls the second carrier injection modulator 3-3 so that its two arms also have a phase difference of 180° and are combined through the second beam combiner 3-7. Finally, the third thermo-optical phase shifter 3-8 makes the phase difference of the two arms 90° and is combined through the third beam combiner. At this time, the entire single-sideband modulator is at the NULL point. At this time, a single-sideband frequency-shifted signal with a high sideband suppression ratio can be generated by inputting two orthogonal signals into the first carrier injection modulator 3-2 and the second carrier injection modulator 3-3 respectively.

[0029] Figure 3 This is a schematic structural diagram of a carrier injection modulator 3-2 in a silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio of the present invention, including a central doped region 3-2-1, an electrode doped region 3-2-2, a heavily doped overlapping region 3-2-3, a terminal resistor 3-2-4, and a single-ended push-pull electrode 3-2-5.

[0030] The carrier injection modulator 3-2 is manufactured using a CMOS process and has a single-ended push-pull structure. The central doped region 3-2-1 is heavily N-type doped with a doping concentration greater than 1e20, and the electrode doped region 3-2-2 is heavily P-type doped with a doping concentration greater than 5e20. To achieve a compromise between high modulation efficiency and low insertion loss, a medium-doped region 3-2-4 with a doping concentration of 1e18 is added, which has a small overlap with the light transmission waveguide region. To achieve terminal matching of high-speed signals, the terminal resistor 3-2-5 is made of TiN material with a resistance of 50 ohms, and the single-ended push-pull electrode 3-2-6 needs to be prepared with differential impedance.

[0031] The present invention uses a carrier injection structure to compress the modulator length to 300μm and reduce Vπ to 1V, while controlling the insertion loss within 1dB. It also integrates functional modules such as thermo-optical phase shifters and monitoring detectors, achieving coordinated optimization of high sideband suppression ratio (>30dB) and low driving voltage, solving the technical bottleneck of traditional solutions in satellite communications and highly integrated systems.

Claims

1. A silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio, characterized in that: include: A first end face coupler (1), serving as an input end coupler, is used to couple an external light source signal to the on-chip waveguide with low loss; A second end face coupler (2), serving as an output end coupler, is used to output the modulated single sideband signal light to the outside of the chip with low loss; A single-sideband modulator module (3), the input end of which is connected to the output end of the first end-face coupler (1), for receiving an input optical signal and performing phase modulation to generate a single-sideband signal with a high sideband suppression ratio; A first-stage unequal splitting ratio beam splitter (4) is used to split the modulated optical signal proportionally, wherein the input end is connected to the output end of the single-sideband modulator module (3), the low splitting ratio end is connected to the monitoring detector (5), and the high splitting ratio end is connected to the silicon optical switch (6); A monitoring detector (5) is used to detect the partial optical signal after the splitting and to feed back the modulation state; The silicon optical switch (6) is connected between the second end face coupler (2) and the first stage unequal split beam splitter (4) and is used to control the flow direction of the modulated signal and select on-chip or off-chip output.

2. The silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio according to claim 1, characterized in that: The single sideband modulator module (3) comprises: A first beam splitter (3-1) is used for evenly splitting the optical signal input from the first end face coupler (1) to two modulation arms; A first carrier injection modulator (3-2) and a second carrier injection modulator (3-3) respectively receive the optical signal split by the first beam splitter (3-1); A first thermo-optical phase shifter (3-4) and a second thermo-optical phase shifter (3-5) are respectively used to control the phase difference between the two arms of the first carrier injection modulator (3-2) and the second carrier injection modulator (3-3) to be 180°; A first beam combiner (3-6) and a second beam combiner (3-7), respectively used to combine the output signals of the first carrier injection modulator (3-2) and the second carrier injection modulator (3-3); A third thermo-optical phase shifter (3-8) is used to control the phase difference of the two combined signals to be 90°; The third beam combiner (3-9) is used for final beam combining and outputting a single-sideband frequency-shifted signal.

3. The silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio according to claim 2, characterized in that: The first carrier injection modulator (3-2) and the second carrier injection modulator (3-3) both adopt a single-ended push-pull structure, comprising: The central doping area (3-2-1) is heavily N-type doped with a concentration greater than 1e20cm -3 ; The electrode doping area (3-2-2) is heavily doped with P-type, with a concentration greater than 5e20cm -3 ; Heavily doped overlapping region (3-2-3) with a doping concentration of 1e18 cm -3 , used to balance modulation efficiency and insertion loss; Terminal resistor (3-2-4), made of TiN material, with a resistance of 50Ω, used for high-speed signal matching; Single-ended push-pull electrode (3-2-5) for differential drive signal input.

4. The silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio according to claim 2, characterized in that: The output light field of the single-sideband modulator module (3) satisfies the following formula: AND out =And in / 2*(and jφ1(t) +e jφ2(t) ) When φ1(t)=φ2(t) in frequency and the phase difference is 90°, a high sideband suppression ratio is achieved; When the splitting ratio γ and phase shift Δθ are considered, the output light field further satisfies the following formula: THAT out =2*E in [γe jφ1(t) +(1−γ)e jφ2(t) ]·that jΔθ 。 5. The silicon-based single-sideband modulator chip with low driving voltage and high sideband suppression ratio according to claim 2, characterized in that: The monitoring detector (5) is used to monitor the working state of the modulator in real time, and adjust the thermo-optical phase shifter through an external control algorithm so that the system works at the NULL point to optimize the sideband suppression ratio.

Images